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In a common type of mechanical ratchet, back and forth motion provided by a human arm gets converted to rotating motion that acts to tighten a screw or bolt. The role of the ratchet is to convert a force that changes direction into a torque acting in one direction only. That principle is generalized in many other systems that convert fluctuations (some of which may be random) into usable work. Many types of ratchets exist, in mechanical, quantum, and biological systems.

Researchers have now fabricated a magnetic quantum ratchet out of graphene, a two-dimensional hexagonal lattice of carbon atoms. C. Drexler and colleagues introduced asymmetries in the electronic structure by disrupting graphene's structure with hydrogen and modifying the substrate on which the carbon sat. When they exposed the modified graphene to an alternating electric current and a strong magnetic field, its electrons preferentially moved in one direction, setting up a directed current. So the modified graphene acted as an AC/DC converter. Although it's not practically useful, the behavior may tell us more about the rules that govern graphene-like materials.

Under ordinary circumstances, graphene is a symmetrical hexagonal lattice of carbon atoms. When exposed to an alternating electric current, the electrons oscillate, producing no direct current on average. Similarly, imposing a steady magnetic field in the presence of the alternating current alters the electronic properties of the graphene slightly, but doesn't tend to make the electrons move preferentially in one direction.

However, the researchers found that introducing even a relatively small number of hydrogen atoms on top of the graphene changed the situation. The same oscillating electric current and steady magnetic field produced a regular flow of electrons. They found a similar effect by modifying the substrate—the material underlying the graphene lattice.

The reason for this striking change in behavior is due to what's called a structure inversion asymmetry in graphene. In the presence of an external influence—in this case, the introduction of hydrogen atoms and a strong magnetic field—the shape of the electron orbits in the carbon atoms gets distorted in one direction. When exposed to the oscillating electric field, the electrons felt a strong resistive force in one direction (which the authors liken to friction), but increased mobility in the opposite direction.

In the analogy used in the research paper, the alternating current acts like the wheel of the ratchet, while the distorted electron orbits act like the pawl, which stops the ratchet from rotating in one direction but not the other. Due to its source and character, in graphene this is known as a magnetic quantum ratchet.

Given how simple it is as a substance, the existence of a structure inversion asymmetry is potentially interesting for understanding graphene's novel electronic and magnetic properties. Other systems exhibiting such behavior are three-dimensional lattices, while graphene is two-dimensional. The authors proposed examining other graphene-like two-dimensional structures, such as boron nitride.

As a practical means of making direct current out of oscillating electric currents, this experiment leaves much to be desired. The electric current was from a 3.34 terahertz (3.34 THz, or 3.34 × 1012 Hz) electromagnetic wave, which falls at the border between microwave and infrared light; household alternating current in the US is 60 Hz. Similarly, the magnetic field the researchers used was 7 teslas, more than twice the strength of a powerful MRI magnet.

However, the purpose of this experiment was the exploration of the electronic properties of graphene, not direct application. Nevertheless, the hidden structure inversion symmetry could help us understand some of the material's behavior, and pave the way to improved magnetic and electron-spin technology that uses graphene and graphene-like substances.

I don't' understand why bloggers insist on simply making up uses for new words and sensationalizing every topic.

This isn't a magnetic quantum ratchet - it's a quantum ratchet. It only WORKS in a magnetic field, but it isn't magnetic.

It isn't even a ratchet - it's a quantum AC/DC converter. They propose a new use for the term ratchet, and it is useful in explaining how the device works to a layman, but you decided to take it a step further. Also, you refer to a ratcheting socket wrench as a ratchet in the first line of your article - it's a wrench that features a ratchet, not a ratchet.

Sigh. It's a shame, you were close, but I guess you or some editor couldn't resist temptation.

I don't' understand why bloggers insist on simply making up uses for new words and sensationalizing every topic.

This isn't a magnetic quantum ratchet - it's a quantum ratchet. It only WORKS in a magnetic field, but it isn't magnetic.

It isn't even a ratchet - it's a quantum AC/DC converter. They propose a new use for the term ratchet, and it is useful in explaining how the device works to a layman, but you decided to take it a step further. Also, you refer to a ratcheting socket wrench as a ratchet in the first line of your article - it's a wrench that features a ratchet, not a ratchet.

Sigh. It's a shame, you were close, but I guess you or some editor couldn't resist temptation.

Actually, the term "ratchet" is used in a very general term in many different professions and it applies just fine to this context.

A bit off-topic: Since we so seldom hear about the substrate and its effect on the experiment, as someone in a completely different field I wonder what the standard substrate is. Must be something really "boring" as is non-reactive, non-conductive, etc.

I don't' understand why bloggers insist on simply making up uses for new words and sensationalizing every topic.

This isn't a magnetic quantum ratchet - it's a quantum ratchet. It only WORKS in a magnetic field, but it isn't magnetic.

If you'd bothered to find the paper involved (i realize that the DOI isn't working yet) you'd find "magnetic quantum ratchet" is used in the title itself. Try to direct your outrage more carefully in the future.

I don't' understand why bloggers insist on simply making up uses for new words and sensationalizing every topic.

This isn't a magnetic quantum ratchet - it's a quantum ratchet. It only WORKS in a magnetic field, but it isn't magnetic.

If you'd bothered to find the paper involved (i realize that the DOI isn't working yet) you'd find "magnetic quantum ratchet" is used in the title itself. Try to direct your outrage more carefully in the future.

I would go further and suggest a careful evaluation of the worth of pedantic 'raging' against such trivia in the first place.

I would go further and suggest a careful evaluation of the worth of pedantic 'raging' against such trivia in the first place.

I'd recommend that they instead direct their pedantry at the concept of pedantry itself, and how it applies to words with multiple context-dependent applications. Which, from its recursive self-referential nature, might be taken as a subtle suggestion for rectal-cranial insertion.

I agree that for now, this isn't practical for most uses out of the terahertz radar range. But also remember that when quantum computing was first explored in a mathematical paper, just for the purpose of understanding the math and quantum effects, it was stated by several authorities, that it would be impossible to do. However, before too long, a quantum computer will be introduced somewhere.

The interesting thing about basic science and technology is that there often seems to be ways around limitations, as long as those limitations aren't built into the theory itself. I wouldn't be surprised if someday, clever people will find ways around this limitation as well.

As a practical means of making direct current out of oscillating electric currents, this experiment leaves much to be desired.

How is this not useful? Do you realize what you could do with transforming infrared waves (heat) into DC current?

In a 7 Tesla magnetic field. Perhaps I can focus rare earth magnets with a clever armature to get there (I have no idea - someone illuminate). Otherwise, you're going to need a hell of a lot of power to run your electromagents. So, not a very useful engineering demonstration. Very cool as a science project (especially since it's 2D) which I believe is the takeaway from the article.

In a 7 Tesla magnetic field. Perhaps I can focus rare earth magnets with a clever armature to get there (I have no idea - someone illuminate). Otherwise, you're going to need a hell of a lot of power to run your electromagents. So, not a very useful engineering demonstration. Very cool as a science project (especially since it's 2D) which I believe is the takeaway from the article.

I somehow did miss the enormous magnetic field on the first read-though. But the ability to transform THz waves into DC will be quite useful.

Both analogies; one to a diode and the other to a bridge rectifier are useful. One diode does not rectify AC into DC but 4 do. Is this illustration of an automotive type, full wave bridge is flawed?

One diode in line with AC current would produce a pulsing DC current because it would only rectify one half (upper or lower, depending on how the diode is oriented) of the AC wave.

A bridge rectifier would rectify both upper and lower wave and the result is dirty DC and rises and falls.

Then add an electrolytic capacitor to smooth out the dirty DC and you got yourself a useful DC power source.

For even smoother DC, add active components (xener diode and transistors or a packaged regulator) to regulate the DC output.

ASCII ART TIME! (Note the leading and trailing lines represent the X axis, the zero potential.)

AC waveform: ---- /\/\/\/\/\/\ ----Rectified with one diode: ___/\_/\_/\_/\___ Rectified with a bridge: ___/\/\/\/\/\/\___Add an electrolytic capacitor to smooth that out and: ___ ------------------- ___

I'm not quite grasping it. Is this a standard tool with fitted, highly experimental "quantum" technology that happens to be a switch to change direction of torque? Like a traditional solenoid-like replacement?

As a practical means of making direct current out of oscillating electric currents, this experiment leaves much to be desired.

How is this not useful? Do you realize what you could do with transforming infrared waves (heat) into DC current?

In a 7 Tesla magnetic field. Perhaps I can focus rare earth magnets with a clever armature to get there (I have no idea - someone illuminate). Otherwise, you're going to need a hell of a lot of power to run your electromagents.

Not so much, a superconducting magnet requires no additional current to run. Eventually you'll need to replace the energy used by whatever you're doing with it, but the steady state field consumes no power.

Quote:

So, not a very useful engineering demonstration. Very cool as a science project (especially since it's 2D) which I believe is the takeaway from the article.

OK, guys, it is a rectifier, single pole or single phase. But cute never the less. A diode rectifies the current and then we start building circuits and so forth. Understanding the effect of doping the graphene and then applying the magnetic field then leads you to some new territory and that is what it is all about. We wait until someone figures out how to do it with a much, much, smaller field, then it gets really interesting.

The electric current was from a 3.34 terahertz (3.34 THz, or 3.34 × 1012 Hz) electromagnetic wave, which falls at the border between microwave and infrared light; household alternating current in the US is 60 Hz

Instead of electromagnetic wave do you mean frequency? Current is moving electrons/electron holes.

Electromagnetic radiation, including both microwave and infrared light, is photons.

I can give better feedback after reading the article (Edit: after it is released).

Given that the purpose of the magnetic field is to distort the electron orbits, which is what creates the ratchet, I don't hold much hope for reducing the staggeringly high field strength. A reduced magnetic field would give a less effective ratchet - ie a leaky diode which lets current through in both directions.

Even under quantum principles where electrons are just clouds of probabilities, the function of the magnetic field is to distort the probabilities to one side / direction, hence the same dismal outcome with a reduced field.

Yes, it sounds like they dressed up the name, but this sounds like a plain diode. Not to say that this isn't interesting. I'm not a graphene guru, but it seems to me that this device doesn't suffer (or at least not as badly) from some of the nonidealities of a semiconductor (as opposed to quantum) diode such as forward voltage drop and reverse recovery time. Of course this comes with the aforementioned 7T tradeoff.

Not to add to the pedanticism here, because there seems to be enough of that to go around, but it's 7 Teslas, not 7 Gauss.

Whoops. I don't even know what a Gauss is. (Something to do with degaussing a monitor?) <- showing my age here

A quick wiki later, and yes it's to do with magnetic field strength. Just another name for Tesla in a different system of measuring. 10,000 Gauss = 1 Tesla. So 7 tesla is 70,000 gauss. I'm on the right track, only out by ~4 orders of magnitude